The present invention relates to a data communication system that sends and receives data to or from an application server via a transmission line comprising one type of a wire communication network, a wireless communication network, and both a wire communication network and a wireless communication network. More particularly, the present invention relates to a data communication system and a data communication method not affected by transmission line characteristics.
Recently, as the Internet technology has become widely used, the user accesses the Internet from a data communication terminal in a variety of ways.
Conventionally, the user accesses the Internet, in most cases, via a wire communication network such as a LAN (Local Area Network) in which terminals are connected by Ethernet or via a wire communication network in which telephone lines and modems are used. Today, in addition to access via those networks, more and more users access the Internet via both a wireless communication network, such as PHS (Personal Handy Phone System) and PDC (Personal Digital Cellular), and a wire communication network.
The only requirement for accessing the Internet is that the IP (Internet Protocol) must be used for the communication protocol hierarchy (layer) that provides data communication terminals with the terminal-to-terminal data transfer function. It is requested to transmit data as effectively as possible on a transmission protocol hierarchy layer in the communication protocol hierarchy. For increased efficiency, many transmission protocols are proposed.
A transmission protocol for accessing the Internet in a wire communication network is optimized for the characteristics of the configuration of a wire network in which a plurality of LANs are connected via routers. The protocol is designed for providing best performance in such a wire network.
On the other hand, a transmission protocol for accessing the Internet in a wireless communication network is optimized for the characteristics of a wireless network that has a large data transmission delay and a narrow transmission bandwidth, so that the protocol is designed for providing best performance in such a network.
Under the conditions described above, a data communication terminal efficiently accesses the Internet using the same protocol via one of a wire communication network, a wireless communication network, and both a wire communication network and a wireless communication network in one of the following methods:
(1) Install both transmission protocols on a data communication terminal, which are switched depending upon the transmission line to be used.
(2) Install the transmission protocol optimized for one type of communication networks, wire or wireless. The effect of the characteristics of the other communication network is suppressed.
First, the former (1) has a problem that increases the amount of memory resources of the data communication terminal, increases the terminal size, and therefore makes the terminal impractical. The latter (2) has a second problem that significantly decreases the throughput of the other, non-optimized communication network and therefore requires positive unit for suppressing the effect of the characteristics of the other communication network.
According to the investigations toward the present invention, the following analyses are given to the conventional art.
In solving the above problems, there are two factors that are affected by the characteristics of a wire communication network and a wireless communication network. One is the server processing time (RTT: Round Trip Time) that determines the time that is set in the retransmission timer. The other is the amount of free space in the receiving buffer at the destination that determines the sending buffer size.
FIG. 8 is a diagram showing the amount of the free space in the receiving buffer at the destination. As shown in the figure, when a data communication terminal sends or receives data to or from an application server (AP server) using the same protocol via a transmission line over one of a wire communication network, a wireless communication network, and both a wire communication network and a wireless communication network, the amount of free space in the receiving buffer at the destination affects the transmission speed of the communication network and the processing speed of the destination terminal.
That is, in case where the sending data communication terminal determines the sending buffer size based on the amount of free space of the receiving buffer of the destination AP server, the above-described first problem of allocating unnecessary memory resources arises if the communication network speed is lower than the processing speed of the destination terminal.
FIG. 9 is a diagram showing the relation between the application server processing time and the retransmission time. As shown in this figure, when the data communication terminal sends or receives data to or from the application server using the same protocol via a transmission line in one of a wire communication network, a wireless communication network, and both a wire communication network and a wireless communication network, the AP server processing time (RTT) is closely associated with a transmission delay (or none) caused by data errors on the communication network and with the retransmission time (timer). Therefore, an improper retransmission timer value, if set, would result in an incorrect data-loss detection and an unnecessary retransmission of a packet or in an unnecessary suppression of packet retransmission, thus generating the second problem which decreases throughput significantly. In other words, when a value that is set in the retransmission timer is too small, a data loss is detected mistakenly and an unnecessary packet or packets is retransmitted. Conversely, when a value that is set in the retransmission timer is too large, a data loss cannot be detected even if generated and so the retransmission of a packet or packets is delayed.
Thus there is much to be desired in the art.
In view of the foregoing, it is an object of the present invention to provide a data communication system and a data communication method not affected by the transmission line characteristics when data is transferred between a data communication terminal and an AP server using the same protocol via a transmission line comprising one of a wire communication network, a wireless communication network, and both a wire communication network and a wireless communication network.
To solve the above problems, a data communication system which sends or receives data to or from an application server using the same protocol via a transmission line comprising one type of a wire communication network, a wireless communication network, and both a wire communication network and a wireless communication network is provided. The data communication system comprises a first table containing therein a relation among a service identifier of the application server, a destination address, a communication network type, and a processing time of the application server; and a retransmission timer setting unit which references the first table to find the processing time of the application server based on the service identifier, destination address, and communication network type during transmission or reception of data to or from the application server and sets the time as a retransmission time.
This formulation sets the retransmission timer properly and therefore reduces the possibility of unnecessary retransmission of packets due to an incorrect data-loss detection or the possibility of unnecessary suppression of transmission at retransmission time, significantly increasing throughput.
Preferably, the data communication system further comprises a radio status acquisition unit which acquires a radio wave strength of the wireless communication network and an error rate of data sent to or received from the wireless communication network from a wireless base station connected via a physical line; and a second table containing therein a relation among radio wave strength of the wireless communication network, error rate of data sent to or received from the communication network, the communication network type, and communication network transmission speeds, wherein the retransmission timer setting unit references the second table, calculates the transmission/reception time for each packet size based on the radio wave strength and the error rate acquired from the radio status acquisition unit, and sets a sum of the processing time of the application server and the calculated transmission/reception time of the packet as a retransmission timer value.
This formulation allows a retransmission timer value to be set according to the transmission line characteristics.
In addition, the present invention provides a data communication system which sends or receives data to or from an application server using the same protocol via a transmission line comprising one type of a wire communication network, a wireless communication network, and both a wire communication network and a wireless communication network. The data communication system comprises (a) a variable-length sending buffer in which data to be sent to the application server is stored; (b) a table containing therein a relation among radio wave strength of the wireless communication network, error rates of data sent to or received from the communication network, communication network types, communication network transmission speeds, and sizes of the sending buffer; (c) and a buffer size controller which references the table to adjust the size of the sending buffer based on the acquired radio wave strength and the error rate.
This formulation eliminates the need for allocating unnecessary memory resources when the transmission speed of the communication network is lower than the processing speed of the destination terminal.
Preferably, the data communication system further comprises a radio status acquisition unit which acquires the radio wave strength of the wireless communication network and the error rate of data sent to or received from the wireless communication network from a wireless base station connected via a physical line and outputs the acquired information to the buffer size controller.
This formulation allows the sending buffer size to be adjusted according to the transmission line characteristics. That is, when the radio wave strength is low or the data error rate is high, the transmission band of the communication network becomes narrow and so the sending buffer may be reduced in size (or volume).
Preferably, a linking (or relaying) server, which sends or receives data to or from the application server over the wire communication network, divides a connection with the application server into two sub-connections and applies a transmission protocol to each sub-connection.
This formulation reduces the amount of packets that are sent to or received from the wireless communication network.
Preferably, the data communication system further comprises a network interface controller which controls a transmission of a packet to the wire communication network or the wireless communication network and sends information on the type of the communication network, to which the packet has been transmitted, to the retransmission timer setting unit or the buffer size controller.
This formulation allows the retransmission timer setting unit to set a retransmission timer value, and the buffer size controller to adjust the size (or volume) of the sending buffer.
Preferably, the data communication system further comprises a transfer controller which controls establishment of a connection with the application server for use in packet transmission and passes the service identifier and the destination address to the retransmission timer setting unit.
This formulation allows the retransmission timer setting unit to set a retransmission timer value.
Preferably, the communication network type (or species) contained in the table comprises only the wireless communication network type.
Because the wireless communication network is easily affected by the transmission line characteristics, eliminating this effect makes the table configuration simpler.
In addition, the present invention provides a data communication system which sends or receives data to or from an application server using the same protocol via a transmission line as one type (species) of a wire communication network, a wireless communication network, and both a wire communication network and a wireless communication network. The data communication system comprises: (a) a first table containing therein relation among service identifiers of the application server (s), destination addresses, communication network types, and processing time of the application server;
(b) a retransmission timer setting unit which references the first table to acquire the processing time of the application server based on the service identifier, destination address, and communication network type during transmission or reception of data to or from the application server and sets the time as a retransmission time;
(c) a variable-length sending buffer in which data to be sent to the application server is stored;
(d) a second table containing therein the relation among radio wave strength of the wireless communication network, error rates of data sent to or received from the communication network, the communication network types, and communication network transmission speeds; and
(e) a buffer size controller which references the second table to adjust size of the sending buffer based on the acquired radio wave strength and the error rate.
This formulation sets the transmission timer properly and therefore reduces the possibility of unnecessary retransmission of packets due to an incorrect data-loss detection or the possibility of unnecessary suppression of transmission at retransmission time, significantly increasing the throughput. At the same time, when the transmission speed of the communication network is lower than the processing speed of the destination terminal, there is no need for allocating unnecessary memory resources.
This enables a data system not affected by transmission line characteristics to be built.
In addition, according to a further aspect of the present invention, there is provided a data communication method for sending or receiving data to or from an application server using the same protocol via a transmission line comprising one type of a wire communication network, a wireless communication network, and both a wire communication network and a wireless communication network. The data communication method comprises the steps of: (a) storing relation among service identifiers of the application server, destination addresses, communication network types, and processing time of the application server in a table; and
(b) referencing the table to set the processing time of the application server as a retransmission time based on the service identifier, destination address, and communication network type during transmission or reception of data to or from the application server.
This method sets the transmission timer properly and therefore reduces the possibility of unnecessary retransmission of packets due to an incorrect data-loss detection or the possibility of unnecessary suppression of transmission at retransmission time, significantly increasing throughput.